1. Field of the Invention
The present invention relates to a linear motion guide unit having wide application in sliding parts incorporated in, for example, assembling machines including semiconductor manufacturing equipments and so on, numerically controlled machine tools, measuring instruments, testing machines and the like. More particularly, it relates to a linear motion guide unit in which a slider is forced to move lengthwise along a track rail.
2. Description of the Prior Art
Linear motion guide units have been universally recognized for fundamental and versatile means to more encourage the recently remarkable growth of mechatronics. Although the linear motion guide units have been extensively built in machinery in fields as diverse as assembling machines including semiconductor manufacturing equipments and so on, numerically controlled machine tools, measuring instruments, testing machines and the like, the expansion of uses accompanied by the current developments in advanced technologies requires more and more such linear motion guide units that can manage growing demands for high precision, low-frictional resistance, high-speed moving, easy assemblage, versatility and the like.
There is conventionally known a linear motion guide unit of the sort disclosed in, for example Japanese Patent Laid-Open No. 11-30234, which is a co-pending application filed by the present assignee. With the prior linear motion guide unit or slider unit, a recirculating-ball screw is accommodated in a track rail of U-shape in cross section and an upper seal is provided to close a clearance left between an upper face of a raceway groove on a slider and the track rail. Moreover, the track rail in the prior linear motion guide unit recited just above is composed of a pair of widthwise opposing sides and a bottom joined together to form an upward opened recess of U-shape in cross section, while the track rail remains left coarse on its inside surface coming in sliding engagement with the lip of the upper seal mounted on the slider. This means it is very tough to move smoothly the slider, so that the sealing effect would be vulnerable.
Japanese Patent Laid-Open No. 2001-12465, which is also a co-pending application filed by the present assignee, discloses another example of the linear motion guide unit having the track rail of U-shape in cross section, which has the widthwise opposing sides made on inside surfaces thereof with raceway grooves. With the prior linear motion guide unit stated earlier, the track rail and the slider are respectively made on their sides with surfaces of reference, which are instrumental in setting the track rail and the slider on any machine bed and table in their precise positions respectively, keeping the working table against any deviation in position and any change in posture with respect to the machine bed. The track rail is fixed to the machine bed with fastening bolts, with the side and bottom surfaces of reference coming into face-to-face abutment to their associated mating side and top surfaces of the machine bed, one to each mating surface, in their precise positions. The slider is also mounted at a slider head thereof to the working table with fastening bolts, with the side and upper surfaces of reference being brought into face-to-face engagement with their associated mating side and lower surfaces of the table, one to each mating surface, in their precise positions.
In a current reality, moreover, the linear motion guide unit is expected to be less expensive, even with high precision. With the linear motion guide unit of the sort constructed as disclosed in the reference cited earlier, the convexities bulged sidewise out of the sides of the track rail is small or narrow in width. This means that the track rail is unsteady in machining and, therefore, too troublesome in machining process to process it with accuracy. In particular, the rolling elements or balls, as could not be kept in place with the slider of itself, would come apart after the slider has been demounted from the track rail. Thus, the slider, just after taken apart from the track rail, has to be transferred to any dummy track rail of U-shape in cross section, which has been ready in advance for replacement for real one. This means that mounting the linear motion guide unit onto various machines needs many chores for handling work of the linear motion guide unit.
Combination of a track rail 61 and a slider 62 as shown in FIG. 16, moreover, has been known for the linear motion guide unit. The track rail 61 has a pair of widthwise opposing sides 63 extending in parallel with one another, which are made outside thereon with lengthwise raceway grooves 67, one to each side. The track rail 61 is made therein bolt holes 66 open to a top face 65 thereof, which are used to fasten the track rail 61 to a machine bed, and so on. The slider 62 fits over the top face 65 of the track rail 61 and conforms in cross section to the track rail 61, and also made up of a carriage 64, end caps 68 attached on forward and aft ends of the carriage 64, one to each end, and end seals 69 arranged on outside ends of the end caps 68 to close clearances left between the end caps 68 and the track rail 61. The end caps 68 together with the end seals 69 are fastened to the carriage 64 with screws that extend across through-holes 86 into fastening holes 92. Lower seals 72 are laid to extend underneath both the carriage 64 and the end caps 68. The carriage 64 is moreover made with raceway grooves 73 extending forward-and-aft in opposition to the raceway grooves 67 on the track rail 61, and also made therein threaded holes opened to a top surface 75. The slider 62 is allowed to move in a sliding manner relatively to the track rail 61 by virtue of rolling elements 78 or balls that rolls through a load raceway 77 defined between the raceway groove 67 of the track rail 61 and the confronting raceway groove 73 on the carriage 64. A retainer band 78 is arranged to fit in a lengthwise relief flute 70 cut deeply into the raceway groove 67 on the track rail 61, continuing to keep the rolling elements 78 in the carriage 64 even after the slider 62 has been taken apart from the track rail 61. The rolling elements 78 are incorporated in the linear motion guide unit in a way rolling through a recirculating circuit that is comprised of the load raceway 77, and a non-loaded area including a return passage 80 formed in the carriage 64 and turnarounds made in the end caps 68 to communicate the return passage 80 with the associated load raceway 77. The slider 62 has a grease nipple 74 for applying lubricant to the recirculating circuit, which is attached to any one of the end caps 68, with extending outside from the associated end seal 69.
The slider 62 with the retainer band 79 is common in the linear motion guide unit of the type in which the slider 62 fit over astride the track rail 61. With the linear motion guide unit constructed as stated earlier, the lengthwise relief flute 70 to fit snugly the retainer band 79 therein is cut in the sidewise opposite outside surfaces 63 on the track rail 61 of rectangular shape in cross section. As the raceway grooves 67 are cut in the lengthwise sides 63 or the external areas of the track rail 61, imparting specific forms including the raceway grooves 67 and the deep relief flutes 70 to the lengthwise sides or the external surface areas of the track rail 61 can be easily realized by just moving a grinding wheel large in diameter against the associated external surface area in a direction at right to the external side 63. Moreover, the lengthwise relief flute 70 to fit the retainer band 79 therein can be readily produced to a desirable specific form.
With the track rail of the sort in which sidewise spaced upright side walls are joined together along their lengthwise underside edges through a lengthwise bottom to form an U-shape in cross section, by the way of contrast, the raceway grooves must be cut in sidewise opposing inside surfaces of the upright side walls, to which the grinding wheel is less accessible compared with the externally exposed outside surfaces. To manage the design consideration as stated earlier, the large-size grinding wheel to produce the raceway grooves on the side walls must enter between the confronting upright side walls in a tilting posture to work around the side walls. Cutting the relief flute to fit the retainer band in there has been proven even tougher because the relief flute has to be cut in the depths or the bottom of the raceway groove. The second alternative would be considered that the relief flute is cut prior to hardening process with the use of any cutter small in diametral size. Nevertheless, it is a disadvantage of the alternative stated just earlier that the relief flute could not be cut with precision throughout the overall length because the track rail is too long to ignore the stress or the like, which is largely the result of previous hardening steps. This has been proven to give rise to a major problem that the relief flute would be made unnecessarily large in dimension to avoid coming into interference with the retainer band, resulting in getting the side walls of the track rail small or weak in strength in traverse direction.
With the linear motion guide unit having the track rail of U-shape in cross section made overall shrunk in construction, it still remains a major challenge to realize how to secure an area in the track rail to fit the retainer band into there without any occurrence of interference between the track rail and the retainer band out when the slider travels along the track rail. Moreover, it has been expected to more quickly and precisely mount the worktable to the slider and also the stationary bed to the track rail respectively at a preselected mounting position and posture, and further make certain that the slider may move relatively to the track rail in a smooth sliding manner with less friction whereby the slider and the track rail are ensured to keep their mounting positions and postures preselected with respect to, for example the worktable and the machine bed, respectively, even after a prolonged period of use.